I uploaded my first real app yesterday, and have had seventy people
hit it. Everything seems to be working like a charm, but those nasty
little average CPU warnings got me worried. My app uses memcache
aggressively, does very few datastore writes, and no page does
extensive processing, so I was surprised to see any warnings.
According to a post I found, I can have two requests of over 1000Mc a
minute, before Appengine starts raising quota exceptions. It also said
that the dashboard figure included datastore megacycles which aren't
included in the quota calculations, and that the log gives accurate
calculations.

So I did some analysis of the logs. Out of more than 700 non-static
requests, there were 9 high CPU warnings. The URLs that triggered
warnings were pretty diverse, including some that do very little work,
and other hard working pages haven't figured yet. Four were for the
same URL, which logged four events, and in each case there was a long
(0.5 to 1sec) delay between two of the events - but two different
events each time. In one case it was after the request has started but
before the first event, and in another it was between the second and
third events, etc. I.e. the delay was not always at the same part of
the code - it wasn't datastore or memcache calls that caused it.

I don't have enough data to be completely certain, but it seems that
there are fairly random 0.5 to 1 second "blips" that occasionally hit
my application, and cause CPU warnings. I could imagine these are
caused by the OS or other applications, and my concern is that my
application could get quota exceptions that are not caused by external
factors. And when billing arrives, I'll get charged for them instead.

Questions:
1. Has anyone else seen this behaviour? Is everyone getting occasional
CPU warnings, and is anyone getting actual quota exceptions because of
them?

2. Has Google any idea what is causing the blips?

Apart from this, I've enjoyed app engine - once little niggles like
this are ironed out, it is going to be a great platform. Can't wait
for it to come out of preview.
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